The present invention relates to a load/unload mechanism for a magnetic head, or in particular to the operation of controlling the load/unload mechanism smoothly by acquiring information from magnetic disk media.
A magnetic disk drive is a peripheral device in which a magnetic head writes (records) or reads (reproduces) information into or from at least a rotating magnetic disk medium for exchanging the information with a host system. In the case where the information is not exchanged, a slider having the magnetic head mounted thereon is undesirably kept on the magnetic disk media at the risk of the slider and the magnetic disk media coming into collision with each other under an external shock that may deteriorate shock resistance performance. On the other hand, the method of keeping the slider in a predetermined area of the magnetic disk media when the media stop rotating (contact start-stop (CSS)) is also undesirable as an adhesion would develop between the slider having the magnetic head mounted thereon and a specific magnetic disk medium.
In view of this, the magnetic disk drive has recently come to employ a load/unload technique for withdrawing the slider (magnetic head) outside of the magnetic disk media. In the load operation, the magnetic head is moved onto the magnetic disk media from the position where it is withdrawn and held, while in the unload operation, the magnetic head is moved to the position outside the magnetic disk media where it is withdrawn and held.
A technique for controlling the movement of the magnetic head by detecting the loading position of the magnetic head from the data recorded on the magnetic disk media is disclosed in JP-A-11-96708. This technique is such that in the loading process, the moving speed of the magnetic head is suppressed or the magnetic head is stopped thereby to prevent the collision between the magnetic head and the magnetic recording media.
In the unload operation for withdrawing the magnetic head from the surface of the media, on the other hand, an actuator having the slider mounted and supported thereon slows down or temporarily stops due to external forces extremely increased when a part of the slider support members including the suspension for supporting the slider rides over the ramp. In order to prevent this inconvenience caused by the movement of the actuator, the speed at which the slider support members run into the ramp at the time of unloading is set to a value considerably larger than the theoretical target speed. In this way, the movement of the slider for the load/unload operation has conventionally been controlled only roughly. As a result, the inconveniences such as the collision between the slider and the magnetic disk media have often occurred.
FIG. 4 can be used also to explain the prior art.
A part of the support members for the slider that has been in the seek operation over the magnetic disk medium 602 is combined with the ramp, so that the slider is unloaded under the guidance of the ramp. In the process, a part of the suspension constituting the support members runs into the ramp 608, and therefore the external forces 316 increase so sharply that the slider extremely slows down or temporarily stops on the ramp 608.
In order to prevent this phenomenon, according to the prior art, the design speed at which the slider runs into the ramp 608 is set to a value higher than the target speed 503 (324) on the ramp 608. Thus, the detected speed is high like the target speed 322 on the ramp slant surface 305a. As the result of the subsequent extreme change of the external forces 316, the detected speed 504 is decreased below the target speed 503 (detection speed 323), and is seen to take some time (325) before coming to coincide with the target speed 503.
Further, at the gradient change points 307a, 307b, 307c where the gradient of the ramp 608 changes, a speed error occurs between the detected speed 504 and the target speed 503 due to the change of the external forces caused by the gradient change, so that the detected speed is seen to take some time length 326a to 326c before coming to coincide with the target speed 503.
In unloading the magnetic head (slider), a part of the support members including the suspension for supporting the slider is combined with the ramp providing the withdrawal/holding means, and the magnetic head is withdrawn following the action of the particular part of the slider support members riding over the ramp. The reverse is the case for the load operation, in which the slider lands on the magnetic disk medium following the action of a part of the support members sliding down the ramp from the holding position thereof.
Generally, the component parts of the load/unload mechanism including the ramp and the slider having the magnetic head mounted thereon have geometric and mounting tolerances, so that the external forces acting between the ramp and the slider support members vary from one magnetic disk drive to another. In the case where the slider is moved to the ramp with a simple constant value, therefore, the slider would slow down or temporarily stop thereby making it difficult to withdraw it over the ramp at a steady rate.
In the prior art, the slider movement is controlled only roughly in the load/unload operation, thereby leading to such inconveniences as the collision between the slider and the magnetic disk media, the friction between or the wear of the ramp member and the slider support members, the generation of dust, etc.
Also, after the slider support members run into the ramp, the slider separated from the magnetic disk media at an insufficiently high position of the ramp collides with the magnetic disk media under a separation shock.
Further, the accurate velocity control operation has not been performed in spite of the need thereof for withdrawing the slider at a steady rate in the unload operation. Thus, the magnetic head sometimes misses the servo information in an area on the magnetic disk media where no servo information is written, with the result that the slider support members having the magnetic head mounted thereon and the ramp often collide with each other at a speed higher than the target speed.